One such power steering system is known from German DE-C2 38 44 578, for instance. In this power steering system, two drums of nonmagnetic material are connected to an input shaft and to an output member, respectively. The drums are provided on their circumference with magnetizable media, in such a way to form magnetic north and south poles in alternation. By measuring the difference in the rotary angles of the two drums, the torque is detected, using magnetoresistive elements.
Detecting the torque makes it possible to regulate the servo assistance of an electric steering system. Regulating the servo assistance in an electric steering system purely as a function of torque feels unaccustomed during driving, because different friction conditions prevail then, compared to a hydraulically assisted power steering system. The "feedback" of the steering speed to the steering moment is missing. To overcome this disadvantage, it is necessary to detect the steering speed. For detecting the steering speed, in known electrical steering systems, for instance in German Patent DE-C2 37 11 854, one additional sensor is provided. The sensor has a direct current tachometer generator, for instance, which generates a direct current with a voltage adapted to the steering speed. This kind of steering speed sensor involves relatively major effort and expense for detecting the steering speed.